The Applicant is the owner of the European patent No. EP 1 623 772 granted on 26 Mar. 2008, that discloses a vise for clamping an elongated workpiece to be bent on a bending machine die. The vise comprises a jaw being rotatable about a pivoting end so that the jaw is approachable to and removable from a circumferential groove of the die in order to surround, from opposite parts, an elongated workpiece. The movable jaw is rotated by an operation mechanism comprising a first hydraulic cylinder that is provided with a rack being connected to its cylinder rod, and a pinion being keyed to the movable jaw and meshing with the rack. Once the rotatable jaw has approached the elongated workpiece to be bent, a retaining device being operated by a second hydraulic cylinder is able to grip a jaw retaining end opposite to the jaw pivoting end in order to clamp the elongated workpiece to be bent in a closed position.
In the above cited European patent there are two separated steps, the one being an approaching step to, the other being a clamping step of an elongated workpiece to be bent in a pipe bending machine. This allows an elongated workpiece to be retained with a high reliability in bending operation. However, as the operation mechanism is fixed on a die side and the retaining device is fixed on the opposite die side, the vise is cumbersome especially in its part that is situated in the lower die side. This prevents some design choices to be made, and generally a pipe bending machine increases in size.
The present invention aims to overcome the drawback above mentioned.
In particular, a main object of the invention is to allow a die to be made having a gripping device of the workpiece to be bent, gripping device that operates with a jaw having two separated approaching and clamping steps, without requiring parts of the gripping device of the workpiece to be bent on both sides of the die.